This invention relates to security enclosures or fences with gates. Many areas both indoors and outdoors require enclosures to control access and egress and a variety of gate systems have been developed to allow controlled access or egress. Swinging gates are among the earliest types used, and are still in use in many areas, but require a considerable amount of space in the open position and it is difficult to adapt them for remotely controlled power operation. Sliding gates are more easily adapted for power operation, and are usually supported from below by wheels and/or rails, and/or supported from above by some form of suspension system. However, these forms of suspension or support for the gates contribute to problems in their operation, as explained below.
Many forms of gates or other closures and systems for opening and closing same, including remotely controlled power systems, have been developed and are known in the art. For example, U.S. Pat. No. 471,851 (1892) discloses a trusswork gate sliding between and supported by upper and lower rollers on two separate posts, the movement of the gate being hand-actuated by a pulley and rope system. The gate when extended can be supported by these rollers alone or by an overhead rail, as shown in FIG. 5 of the patent. U.S. Pat. No. 1,639,866 discloses a railroad crossing safety gate suspended from overhead rails which can be moved back and forth by a motorized gear and pinion system.
U.S. Pat. No. 1,731,908 shows a motorized railroad crossing safety gate having separate single-beam gate sections which are driven by rack and pinion gearing systems from each side to interlock in the center. Conventional electrical switching and drive systems are used. U.S. Pat. No. 2,746,745 shows a parking lot gate in a fence, suspended from an overhead rail and moved in either direction by a motorized pulley-cable system. Conventional electronic card-key systems are used for opening and closing the gate. The overhead rail, drive and suspension systems must all be positioned high enough above ground level to permit the passage of any vehicle authorized to use the area, requiring excessive overhead clearance if installed in indoor areas. U.S. Pat. No. 4,065,878 shows a trusswork-type gate operating on a lower rail and supported on small wheels, having a friction drive on the top of the gate which can be disengaged for manual use of the gate. Guide wheels are provided on each side of the top member of the gate to stabilize the friction drive. The friction drive system is positioned on a post standing beside the gate. Detecting means can actuate the drive to open or close the gate, or a remote switch can be used. An "overload protector" stops the drive if an object or a person interferes with the movement of the gate.
Despite the extensive development of gates and other closure means over the years, the need is apparent for further improvements to alleviate problems with existing sliding gates which move parallel to the fence or other enclosure means. For example, the various overhead suspension and drive systems which have been used tend to require excessive overhead clearance in order to provide access for vehicles normally expected to pass through the gate, and block vehicles which require greater overhead clearance. On the other hand, the wheels, rails, skids or the like required to provide support for such gates from beneath are easily fouled by dirt, debris, mud, snow, ice or the like, and thus require frequent cleaning and maintenance to operate properly. Although friction drive systems are simple and economical to design and install, their operation is frequently disrupted by motions of the gate during operation, as discussed in U.S. Pat. No. 4,065,878, Column 3. Thus, the need is apparent for gate systems of improved design in which the gate can be suspended in operation without the necessity for obstructive overhead systems or support systems beneath the gate which require extensive cleaning and maintenance to operate properly.
Furthermore, due to various terrorist activities and the encroachment of other criminals upon protected areas both public and private, ranging from cattle ranches to high-priority government installations, security is becoming an increasing concern in modern life. Cattle rustling and horse stealing have become greater concerns than in the Old West and various areas must be protected from unauthorized entry for burglary or other mischief, while allowing convenient controlled access to authorized persons. High priority government facilities such as embassies and defense installations increasingly require protection comparable to that provided by castles of the Middle Ages. Heavy duty fences, barriers and gates are required to prevent unauthorized access by terrorists or criminals, with the threats extending to ramming by large explosive-laden trucks traveling at high speed.